[Smush Pro] Bulk directory smush stops working

I'm trying to run a bulk directory smush on quite a lot of images (almost 4000). The tool keeps getting hung up and stopping. It used to stop at 107 but after a while it moved forward. Now it's stopping at image 809. I left my computer running for 2 hours and didn't move past this point.

Screenshot: https://www.screencast.com/t/q7Qb6a0nTe